ELECTRONIC DESIGN NOTES - RESISTORS

In Electronic Design Notes #1
was mentioned we can control the current passing through electrical circuits using resistors. Of course, there are other means
to achieve good current control, but resistors are simple, cheap, and very efficient electronic components.

Control is the true magic word in electronics. No matter what we do, the purpose is to take control
over voltages,
currents, frequencies, and over various functions. Once we achieve total control, then we can do whatever we can
think of. Resistors help us control all electrical characteristics that
are calculated based on resistance: that is, current, voltage, frequency, etc.

There are a few basic things we need to know about resistors, therefore they are listed summarily as follows:

In Fig 4, we control the voltage Ui using a "voltage divider" schematic.
We can even adjust Ui if we use a potentiometer schematic as we did in in Fig 1. The voltage divider
schematic allows for 2, 3,..n precise voltage levels to be supplied to the
"Load" circuit. In Fig 4 are the formulas
needed to calculate the Ui value.

In Fig 5, R1 plays the role of a "current limiter". The meaning of that schematic is, the maximum
current supplied to Load is 4 mA. Even if Load becomes a short-circuit, the maximum current will not exceed 4 mA.
Please note: using a variable resistor wired as in Fig 1, the Rheostat, we can adjust the maximum/minimum
current supplied to Load.

In both of the above schematics, Figs 4 and 5, we could use programmable potentiometers. Details about the simplest and the most
efficient ways of working with programmable potentiometers are presented in
LEARN HARDWARE
FIRMWARE AND SOFTWARE DESIGN.

In normal conditions V1 = 12 V, and V2
= 11.988 V (R1 = 1 KΩ). These values are sent to the Analog-to-Decimal channels 1 and 2
(randomly chosen) of the PIC controller. Next, we transform the analog voltages into their decimal equivalents, then we compare them
mathematically. The result is one of the following instances:

If an accident happens and Load becomes a generator, the current will change its sense, therefore V2 will become
greater than V1:V2 > V1

Not only that we are able to detect the sense of the current, but we know precisely how much current Load is drawing in
each moment.
Details about working with Microchip dsPIC controllers and about AD conversion are
presented in
LEARN HARDWARE
FIRMWARE AND SOFTWARE DESIGN.